The present invention relates to a method of cleaning a semiconductor processing chamber. More particularly, the present invention relates to a method of protecting quartz hardware from being etched during plasma-enhanced cleaning of a semiconductor processing chamber.
During most semiconductor manufacturing processes, such as dielectric etching or chemical vapor deposition, unwanted materials are sometimes formed on the semiconductor wafers themselves and on the interior walls of the processing chamber. Naturally, it is critical to remove these unwanted materials from the semiconductor wafers. Equally importantly, materials deposited on the interior walls of the processing chamber must also be removed because they may become a source of contaminants. For instance, in dielectric etching, long-chain carbon polymers may build up on the interior walls of the processing chamber. Loose particles of these polymers may break off during the manufacturing process and contaminate the wafers. Thus, in order to increase yield and provide a contaminant-free environment, processing chambers must be periodically cleaned.
Conventionally, processing chambers are cleaned by manual scrubbing. In this conventional method, the manufacturing process has to be halted and the processing chamber opened such that the interior walls may be scrubbed. Consequently, this method is extremely time-consuming and disruptive to the manufacturing process. In addition, the chamber cleaner has to rely on visual inspection to determine whether a processing chamber is clean or not. Sometimes, when manual scrubbing is not thorough enough, the yield of semiconductors subsequently processed will be greatly affected.
Other methods have been proposed to overcome problems with the conventional manual scrubbing method. One such method, which is applicable to removing oxide and dielectric contaminant build-up, involves the use of a plasma-enhanced etching process to xe2x80x9cdry cleanxe2x80x9d the semiconductor processing chamber walls. In that prior art method, fluorine-based gases such as CF4 and CHF3 and oxygen are highly energized to form a plasma which reacts with the contaminants to form CO2, SiF2 and other gaseous compounds which are then vacuumed away through the processing chamber""s exhaust system. Although this prior art method is an improvement over the conventional manual scrubbing method, it is unsuitable for cleaning processing chambers which include quartz hardware. In particular, fluorine plasma formed by fluorine-based gases such as CF4 and CHF3 is very aggressive to quartz. Consequently, the exposed quartz parts of those processing chambers have to be replaced regularly, unnecessarily increasing the semiconductor manufacturing cost.
More importantly, when exposed to fluorine plasma, the quartz hardware of those processing chambers would be etched. As a result, the quartz hardware may become a source of particle contaminants. Such particle contaminants may introduce impurities in the wafers being processed. Thus, yield may be adversely affected.
Therefore, what is needed is a method of providing an ultra-clean environment for a semiconductor processing chamber having quartz hardware. What is further needed is a novel plasma cleaning gas which is particularly applicable to remove polymer and photoresistive contaminant build-up and is quartz-safe.
The present invention is a method of suppressing the etchrate of quartz hardware in a semiconductor processing chamber during plasma-enhanced cleaning. In one embodiment, the method of the present invention comprises the steps of: (a) introducing a mixture of fluorocarbon gas, oxygen, and water vapor into the chamber; and (b) activating the mixture to form a quartz-safe plasma cleaning gas. The plasma cleaning gas then reacts with contaminants deposited on the walls of the semiconductor processing chamber to form gaseous exhaust compounds. The etchrate of the quartz hardware, however, is substantially suppressed by the presence of water in the plasma cleaning gas.
In the present embodiment of the invention, the fluorocarbon gas comprises CF4, In addition, the present invention may be practiced in a plasma etcher where the oxygen/fluorocarbon ratio is 10:1, and having a pressure of 1.2 Torr, a temperature of 200xc2x0 C. and an electrode power of approximately 1000 watts. Further, in the present embodiment, water vapor is introduced at a rate of more than 60 standard cubic centimeters per minute (SCCM).